1. Field of the Invention
This invention relates to a semiconductor device comprising a plurality of functional elements arranged on a substrate.
2. Related Background Art
To date, thin film transistors prepared by using an amorphous silicon thin film for functional elements have a wide variety of applications as switching devices including display devices such as liquid crystal panels and organic EL panels as well as optical sensor panels where they are used in combination with PIN photodiodes comprising an amorphous silicon thin film like TFT elements or photoelectric conversion elements (to be referred to as optical sensor elements hereinafter) such as MIS photocapacitors and TFT optical sensors.
In recent years, efforts have been paid to develop medical applications for optical sensor panels. Particularly, indirect-type radiation imaging apparatus adapted to transform radioactive rays into visible light by means of fluorescent substances to indirectly read the obtained optical information by means of an optical sensor panel and direct type radiation imaging apparatus comprising TFT devices and amorphous selenium to directly transform radioactive rays into electric signals have been developed.
FIG. 15 shows an equivalent circuit diagram of an optical sensor panel comprising TFT elements and PIN photodiodes and FIG. 16 shows a schematic cross sectional view of such an optical sensor panel. In FIG. 15, reference numerals 1010, 1020 and 1030 respectively denote a PIN optical sensor, a TFT and a signal wire, whereas reference numerals 1040 and 1050 respectively denotes a TFT drive wire and a bias wire of the PIN optical sensor.
In FIG. 16, reference numerals 2010, 2020, 2030, 2040, 2050, 2060, 2070 and 2080 respectively denote a glass substrate, a gate wire, a gate insulating film, an i-type a-Si layer, an SiN layer, an n+ ohmic contact layer, a source/drain electrode and a sensor lower-electrode whereas reference numerals 2100, 2110, 2120 respectively denotes P-, I- and N-type a-Si layers. Reference numeral 2090 denotes a sensor upper-electrode and reference numeral 2130 denotes an SiN protection film.
The incoming beam that is carrying image information is subjected to photoelectric conversion by the PIN optical sensor 1010 and its electric charge is stored in a sensor capacity C1. Subsequently, when the TFT 1020 is turned on, the electric charge is distributed to a capacity C2 formed at the crossing of the signal line 1030 and the TFT drive wire 1040 so that the change in the potential of the signal line 1030 is read and output.
Currently, improvements are required of the above-described optical sensor panels in terms of substrate size and process precision in order to meet the demand for a larger display area and a higher degree of definition. However, any such improvements may inevitably entail a huge amount of investment in plant and equipment and a long introductory pre-operational period so that doubts may be cast on such an idea.
In view of this problem, there have been proposed semiconductor devices adapted to produce a large display area by bonding a plurality of relatively small panels. Such semiconductor devices may be realized by using existing plants and equipment for manufacturing small substrates.
FIG. 17 is a schematic perspective view of a radiation image reading apparatus having a large display area and formed by bonding four optical sensor panels. FIG. 18 is a schematic cross sectional view of the device of FIG. 17. In FIG. 17, reference numerals 3010, 3020, 3050, 3060 and 3400 respectively denote an optical sensor panel, a base, a fluorescent panel, a flexible substrate and a chassis.
Referring to FIG. 18, the base 3020 is used to rigidly hold four optical sensor panels 3010 and typically made of lead that absorbs radioactive rays and protects the electric components arranged therebelow. The sensor panels 3010 are bonded to the base 3020 by way of a first adhesive layer 3030, while the fluorescent panel 3050 for transforming radioactive rays into visible light is bonded to the sensor panels 3010 by way of a second adhesive layer 3040. In FIG. 18, reference numeral 3070 denotes a printed substrate for driving the sensor panels and reference numeral 3060 denotes a flexible substrate for connecting the printed substrate 3070 and the sensor panels 3010.
In FIG. 18, there are also shown a cabinet 3200, a lid 3210, a cover 3230 typically made of lead and adapted to protect the electric components, feets 3240 for rigidly securing the printed substrate 3070 and angles 3250 firmly securing the base 3020 to the cabinet 3200. Note that the chassis 2400 comprises members denoted by 3200, 3250. A sensor unit is formed by firmly securing the radiation sensor 3300 within the chassis.
However, when bonding a plurality of panels in a manner as described above, the precision level of the boundaries and that of the clearances separating them are of vital importance.
FIG. 19 is a schematic plan view of four bonded panels. FIG. 20 is an enlarged schematic plan view of a central part of the four bonded panels of FIG. 19, illustrating the boundaries of the panels. In FIG. 20, P denotes the pitch of arrangement of pixels and Pc denotes the distance between the centers of two pixels that belong to different panels and are arranged adjacently relative to each other. In general, correction by way of image processing can properly be carried out, when Pc less than 2P or the clearance between two panels is made to be less than the size of one pixel. In other words, each sensor panel has to be cut with a margin of several tens of micrometers from the edges of the pixels.
Any attempt for meeting the above requirement is accompanied by the problems as listed below and can end up with a poor manufacturing yield and a poor performance unless they are solved to a satisfactory extent.
1. Some of the pixels of an optical sensor panel can be adversely affected by a cutting operation due to problems such as chipping and/or displacement. Then, the reliability of the sensor panel is lowered after assembling. FIG. 21 is a schematic plan view of a cut area of a sensor panel comprising a pixel 4010 and a protection film 4020 typically made of SiN. In FIG. 21, 4030 denotes a notch formed typically by chipping and 4040 denotes an end facet produced by the cutting. As seen from FIG. 21, the protection film 4020 is partly damaged by notches 4030. As a result, although the sensor panel operates properly in the initial stages, it has been confirmed that its output fluctuates when it is subjected to high temperature and high humidity.
2. Pixels can be destructed by static electricity appearing in the course of assembling of the panels. Normally, insulating items such as glass substrates can become electrically charged with ease when peeled off in a vacuum chuck stage and/or scrubbed by blown air. When the panel is just brought close to an object having an electric potential difference such as a grounded cabinet, an electric discharge occurs to destroy some or all of the pixels of the panel, particularly those arranged at the corners. Then, a poor manufacturing yield can result.
3. A pixel of the assembled sensor panels can be destroyed along the cut edges, particularly at the corners, when static electricity is accumulated to 2 to 3 kV in the course of handling the panels in the assembling process.
In view of the above identified problems, it is an object of the present invention to provide a semiconductor device with which a panel having a large area or a narrowly margined panel with the circumferential space minimized can be manufactured stably with a high yield.
More specifically, it is a first object of the present invention to provide a semiconductor device provided with a slice check wire for determining the acceptability of the operation of cutting the panels in order to ensure that the panels to be bonded are cut and bonded accurately, said slice check wire being located at a position with which reliability can be secured to electrically check any possible damages such as chippings to the protection film and other components produced in the cutting process in order to secure the reliability of the product after the assembling process.
A second object of the present invention is to provide a semiconductor device in which any electric cross talks are suppressed by fixing the electric potential of the slice check wire to a constant level.
A third object of the present invention is to provide a semiconductor device having an anti-charge feature for securing the stability and the reliability of the device, which can be achieved by electrically connecting the slice check wire to the drive wires of TFTs or the bias wires of the optical sensor in order to improve the resistance against electrostatic discharge failures and also by fixing the electric potential of the slice check wire to a constant level.
According to the invention, the above objects are achieved by providing a semiconductor device comprising a TFT substrate having a plurality of pixels of a plurality of TFT (thin film transistors) provided on the substrate, slice lines for cutting the TFT substrate being arranged along the periphery of said TFT substrate, peripheral wires being arranged between said slice lines and said TFT substrate.
Preferably, said peripheral wires are connected to at least the drive wires or the signal wires of said TFTs. Preferably, each pixel of said TFT substrate comprises a TFT element and a photoelectric conversion element and said peripheral wires are electrically connected to the bias wires of the photoelectric conversion element.